A fracture model of radiation blistering

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Abstract
The formation process of blisters is interpreted by a fracture model on the basis of the stress fields around a lenticular bubble calculated in a previous paper. This model implicitly presumes a microcrack nucleated at a depth near the projected range of the ions. Two factors are separated theoretically to explain the blister formation: One is a geometrical factor which depends only on the ratio of size to depth, from a free surface, and the other factor is proportional to the square of the ratio between the internal gas pressure of the bubble to plastic yield stress of the target materials, depending entirely on the physical and chemical properties of the materials and gas atoms. The relation between the blister diameter and the cover thickness must be basically linear as expected from the first factor, but is modulated by the second factor, giving a slight departure from linearity as observed by experiment. The ratio of the gas pressure to the yield stress must be 0.02–0.2 in magnitude and depends on the ion energy and the target materials. This value leads to an estimation that the amount of gas atoms contained in the blister is about 10% of the injected ions. Griffith’s criterion for the crack propagation in the subsurface layer with taking into account of ductility of the materials near the crack tip was derived, and showed that the estimated internal pressure of the blister is far smaller than the necessary pressure to satisfy the criterion. The objections against the gas‐pressure model were criticized on the basis of the present model.